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aoc8.go
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aoc8.go
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// aoc8.go --
// advent of code 2022 day 8
//
// https://adventofcode.com/2022/day/8
// https://github.com/erik-adelbert/aoc
//
// (ɔ) Erik Adelbert - erik_AT_adelbert_DOT_fr
// -------------------------------------------
// 2022-12-8: initial commit
package main
import (
"bufio"
"fmt"
"os"
)
// part indices
const (
Part1 = iota
Part2
)
func main() {
counts := [2]int{0, 0}
// store all axis
M := make([][]byte, 0, 128)
input := bufio.NewScanner(os.Stdin)
for input.Scan() {
M = append(M, []byte(input.Text()))
}
W, Σ := mirror(M), transpose(M)
Ͻ := mirror(Σ) // Ͻ reads reverse (lunate) Σ
views := func(x, y int) [4][]byte {
U := Ͻ[x][len(Ͻ[0])-y:] // up
L := W[y][len(W[0])-x:] // left
R := M[y][x+1:] // right
D := Σ[x][y+1:] // down
return [4][]byte{U, L, R, D}
}
// part2
dist := func(o byte, axis []byte) (int, byte) {
var (
acc int
x byte
)
for _, x = range axis {
acc++
if x >= o {
break
}
}
return acc, x
}
for y, r := range M {
for x, o := range r {
seen := false // part1
count := 1 // part2
for _, v := range views(x, y) {
d, h := dist(o, v)
// part1
if !seen && o > h {
counts[Part1]++
seen = true
}
// part2
count *= d
}
// part2
counts[Part2] = max(counts[Part2], count)
}
}
fmt.Println(counts[Part1], counts[Part2])
}
func transpose(m [][]byte) [][]byte {
t := mkmat(len(m[0]), len(m))
for i := 0; i < len(t); i++ {
r := t[i]
for j := 0; j < len(r); j++ {
r[j] = m[j][i]
}
}
return t
}
func mirror(m [][]byte) [][]byte {
t := mkmat(len(m[0]), len(m))
for i := 0; i < len(t); i++ {
r := t[i]
for j := 0; j < len(r); j++ {
r[j] = m[i][len(r)-(j+1)]
}
}
return t
}
func mkmat(h, w int) [][]byte {
r := make([]byte, h*w)
m := make([][]byte, h)
lo, hi := 0, w
for i := range m {
m[i] = r[lo:hi:hi]
lo, hi = hi, hi+w
}
return m
}